Insoluble sulfur generally refers to sulfur insoluble in carbon disulfide. Insoluble sulfur is polymeric in nature, and the polymer chain is made up of up to several thousand sulfur atoms. Insoluble sulfur is widely used as a vulcanizing and crosslinking agent in rubber compound formulations. Insoluble sulfur is produced by the solvent method in which carbon bisulfide is used as the solvent. Carbon bisulfide is inflammable, combustible, hazardous, and poisonous, thus, it requires extreme safety precautions for the production process.
Chinese Patent No. CN201058813Y discloses an integrated treatment apparatus for making insoluble sulfur, including stirring and mixing, slaking, filtering, extracting, and vacuum drying. The apparatus has a porous semi-cylindrical filter screen and a filter plate for filtration, however, the surface area for filtering is inadequate yet the parts occupy large volume in the apparatus with onerous arrangement.
Chinese Patent No. CN201240848Y discloses a multifunctional tank for producing insoluble sulfur. The upper half of the inner space of the outer cylinder in the apparatus functions as an area for passing heating and cooling medium, and the lower half functions as an independent filtering cavity comprised of an inner cylindrical body, an outer cylindrical body, and two partition boards between the middle portion of the two cylindrical bodies. The inner cylindrical body functions as a filter plate in the filtering cavity, and a plurality of porous pressure plates are fixed along the radian inside the inner cylindrical body. The filter screen is arranged between the inner cylindrical body and the pressure plates. The surface area of the apparatus for filtering is inadequate and the speed is slow. These apparatus have the drawback of slow filtering rate, long wash and dry time, and low production efficiency, which make them unsuitable for industrial production.